Some stores will have have a size reference where you can look up your make and model. If they don't you will need to measure the old wiper blade lengths for each side and go by that.
When you go to an auto parts store, they almost always have a book or electronic guide. You simply enter the year, make, and model of your vehicle and it will tell you what size to buy.
This is very simple. Either measure the ones that are currently on your car or look up your vehicle in the book that is provided at most retail stores that sell windshield wipers. Even better, have them swap them out for you at an oil change place.
